| Blood
System. Introduction
Circulation the process by which nutrients, respiratory
gases, and metabolic products are transported throughout
a living organism, permitting integration among the various
tissues. The process includes the intake of metabolic materials,
the conveyance of these materials throughout the organism,
and the return of harmful by-products to the environment.
Invertebrate
animals have a great variety of liquids, cells, and modes
of circulation, though many invertebrates have what is called
an open system, in which fluid passes more or less freely
throughout the tissues or defined areas of tissue. All vertebrates,
however, have a closed system—that is, their circulatory
system transmits fluid throughan intricate network of vessels.
This system contains two fluids, blood and lymph, and functions
by means of two interacting modes of circulation, the cardiovascular
system and the lymphatic system; both the fluid components
and the vessels through which they flow reach their greatest
elaboration and specialization in the mammalian systems
and, particularly, in the human body.
A
full treatment of human blood and its various components
can be found in the article humanblood. A discussion of
how the systems of circulation, respiration, and metabolism
work together within an animal organism is found in the
article respiration.
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